1. Field of the Invention
This invention relates generally to the field of navigation systems and, more particularly, to a method and system for improving the reliability of speech recognition in a vehicle navigation system that uses the concept of phonetic letter families, or groups of similar sounding letters, to improve the accuracy and reliability of machine recognition of spoken addresses for entry of destinations into the navigation system.
2. Discussion of the Related Art
Modern vehicles frequently include onboard navigation systems as a driver safety and convenience feature. The methods by which drivers, or others in the vehicle, interact with the navigation system vary widely from one system to another. Some navigation systems require the user to enter information, such as a destination address, via a touchscreen menu system or keyboard-style screen. These systems have the distinct disadvantage that they cannot be used safely by a driver while driving due to the high level of distraction they cause the driver—including a cognitive load on the driver, and the need for the driver to take his or her hands off the steering wheel and eyes off the road. Another disadvantage of these systems is the added cost due to the requirement of an interactive screen.
An alternative to manually entering data into a keypad or touchscreen is to use voice commands for providing inputs to the navigation system. The use of voice commands to control a vehicle navigation system, for example to designate a destination address, is desirable as discussed previously. However, a significant problem exists with respect to the accurate machine recognition of the spoken words. Speech recognition is particularly challenging in an automotive cockpit environment, due to the high level of background noise which is normally present. Some speech-recognition based navigation systems have attempted to overcome this difficulty by allowing the user to spell their destination street, city, and state names one letter at a time. This approach has the advantage that each sound spoken must only be matched with one of the 26 letters of the English alphabet, rather than checked against the many thousands of names in an address directory. Even these systems, however, have problems discerning the difference between letters which sound alike—such as A, J, and K. Such systems have typically resorted to asking the user to confirm each letter after it is spoken, which adds significant time and aggravation to the process. Furthermore, if these existing systems mistakenly identify even one letter during the spelling process, they are unlikely to be able to accurately match the desired destination name.
Given all of these difficulties with existing speech recognition techniques in navigation systems, a need was recognized for a system which has the advantages of letter by letter spelling, but is more robust in handling the ambiguity caused by letters which sound similar.